package com.chinathinks.core.net.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.PushbackInputStream;

/***
 * This class wraps an input stream, replacing all occurrences of
 * &lt;CR&gt;&lt;LF&gt; (carriage return followed by a linefeed), which is the
 * NETASCII standard for representing a newline, with the local line separator
 * representation. You would use this class to implement ASCII file transfers
 * requiring conversion from NETASCII.
 * <p>
 * <p>
 * 
 * @author Daniel F. Savarese
 ***/

public final class FromNetASCIIInputStream extends PushbackInputStream {
	static final boolean _noConversionRequired;
	static final String _lineSeparator;
	static final byte[] _lineSeparatorBytes;

	static {
		_lineSeparator = System.getProperty("line.separator");
		_noConversionRequired = _lineSeparator.equals("\r\n");
		_lineSeparatorBytes = _lineSeparator.getBytes();
	}

	private int __length = 0;

	/***
	 * Returns true if the NetASCII line separator differs from the system line
	 * separator, false if they are the same. This method is useful to determine
	 * whether or not you need to instantiate a FromNetASCIIInputStream object.
	 * <p>
	 * 
	 * @return True if the NETASCII line separator differs from the local system
	 *         line separator, false if they are the same.
	 ***/
	public static final boolean isConversionRequired() {
		return !_noConversionRequired;
	}

	/***
	 * Creates a FromNetASCIIInputStream instance that wraps an existing
	 * InputStream.
	 ***/
	public FromNetASCIIInputStream(InputStream input) {
		super(input, _lineSeparatorBytes.length + 1);
	}

	private int __read() throws IOException {
		int ch;

		ch = super.read();

		if (ch == '\r') {
			ch = super.read();
			if (ch == '\n') {
				unread(_lineSeparatorBytes);
				ch = super.read();
				// This is a kluge for read(byte[], ...) to read the right
				// amount
				--__length;
			} else {
				if (ch != -1)
					unread(ch);
				return '\r';
			}
		}

		return ch;
	}

	/***
	 * Reads and returns the next byte in the stream. If the end of the message
	 * has been reached, returns -1. Note that a call to this method may result
	 * in multiple reads from the underlying input stream in order to convert
	 * NETASCII line separators to the local line separator format. This is
	 * transparent to the programmer and is only mentioned for completeness.
	 * <p>
	 * 
	 * @return The next character in the stream. Returns -1 if the end of the
	 *         stream has been reached.
	 * @exception IOException
	 *                If an error occurs while reading the underlying stream.
	 ***/
	public int read() throws IOException {
		if (_noConversionRequired)
			return super.read();

		return __read();
	}

	/***
	 * Reads the next number of bytes from the stream into an array and returns
	 * the number of bytes read. Returns -1 if the end of the stream has been
	 * reached.
	 * <p>
	 * 
	 * @param buffer
	 *            The byte array in which to store the data.
	 * @return The number of bytes read. Returns -1 if the end of the message
	 *         has been reached.
	 * @exception IOException
	 *                If an error occurs in reading the underlying stream.
	 ***/
	public int read(byte buffer[]) throws IOException {
		return read(buffer, 0, buffer.length);
	}

	/***
	 * Reads the next number of bytes from the stream into an array and returns
	 * the number of bytes read. Returns -1 if the end of the message has been
	 * reached. The characters are stored in the array starting from the given
	 * offset and up to the length specified.
	 * <p>
	 * 
	 * @param buffer
	 *            The byte array in which to store the data.
	 * @param offset
	 *            The offset into the array at which to start storing data.
	 * @param length
	 *            The number of bytes to read.
	 * @return The number of bytes read. Returns -1 if the end of the stream has
	 *         been reached.
	 * @exception IOException
	 *                If an error occurs while reading the underlying stream.
	 ***/
	public int read(byte buffer[], int offset, int length) throws IOException {
		int ch, off;

		if (length < 1)
			return 0;

		ch = available();

		__length = (length > ch ? ch : length);

		// If nothing is available, block to read only one character
		if (__length < 1)
			__length = 1;

		if (_noConversionRequired)
			return super.read(buffer, offset, __length);

		if ((ch = __read()) == -1)
			return -1;

		off = offset;

		do {
			buffer[offset++] = (byte) ch;
		} while (--__length > 0 && (ch = __read()) != -1);

		return (offset - off);
	}

	// PushbackInputStream in JDK 1.1.3 returns the wrong thing
	/***
	 * Returns the number of bytes that can be read without blocking EXCEPT when
	 * newline conversions have to be made somewhere within the available block
	 * of bytes. In other words, you really should not rely on the value
	 * returned by this method if you are trying to avoid blocking.
	 ***/
	public int available() throws IOException {
		return (buf.length - pos) + in.available();
	}

}
